The risk for developing end-stage renal disease (ESRD) in African Americans is more than 3-fold higher than European Americans. This disproportionate risk is apparent for virtually all forms of kidney disease, but only a minor portion can be explained by socio-economic status and/or poor access to health care. Recent studies have identified polymorphisms in the gene encoding MYH9, a non-muscle myosin heavy chain that are associated with susceptibility to ESRD in African-Americans, explaining a substantial component of the attributable risk. Identification of this association between MYH9 variants and risk for ESRD is a major breakthrough. However, since these variants do not include significant changes in the sequence of exons or intron:exon junctions, the major research opportunity and scientific knowledge gap is to determine the causal mechanisms connecting MYH9 polymorphisms with the pathogenesis of kidney injury. Because MYH9 is a structural, intra-cellular protein, its role in the pathobiology of kidney disease will be difficult to study in patients through analysis of clinical samples. Nonetheless, translating the discovery of this genetic association into improved prevention and treatment for individuals at risk will require precise understanding of the mechanisms whereby these genetic variants influence the course of kidney disease. Accordingly, we propose to generate mouse lines in which human MYH9 haplotypes are inserted into the syntenic location of the mouse genome in the absence of the mouse orthologue. These lines will be generated using a novel and robust 2-step method wherein the mouse locus is excised in embryonic stem (ES) cells in a manner that allows rapid introduction of the analogous human gene directly into the deleted locus. Our experience in developing this method indicates that the inserted human gene retains its key functional and regulatory properties in the mouse. Thus, development of these animal models will provide a unique opportunity for studying the physiological consequences of human MHY9 haplotypes in vivo under precisely controlled genetic and environmental conditions in order to understand their contributions to the development of kidney injury. We have assembled a highly accomplished, multi-disciplinary team to ensure that the generation and initial characterization of these mouse lines can be completed within the two-year period specified by the Recovery Act. These animal models will be powerful tools for identifying new strategies for preventing ESRD in African Americans. PUBLIC HEALTH RELEVANCE: African Americans have a significantly greater risk of developing end-stage renal disease (ESRD) than European Americans. While this disparity has been recognized for some time, its cause was not known. Recently, two groups independently identified associations between risk for ESRD in African-Americans and variations in a gene called MYH9. However, it is not clear how the variation in this gene could lead to kidney disease. In the studies we are proposing, we plan to generate mice in which the human MYH9 variants are inserted into the mouse genome where they can be studied under precisely controlled genetic and environmental conditions in order to understand their contributions to the development of kidney injury. These animal models will be powerful tools for identifying new strategies for preventing ESRD in African Americans.